The present invention relates to a mask structure which used for manufacturing solid-state devices having fine pattern structures such as semiconductor integrated circuit devices and surface acoustic wave (SAW) devices, and a method of manufacturing solid-state devices by using such a mask structure.
Specifically, a SAW device obtained by using the present invention is suitable for use in a communication apparatus such as a radio communication terminal.
In a projection aligner (or a projection type exposure apparatus) a photo-mask or a reticle is illuminated by an illuminating optical system to transfer a circuit pattern onto a photosensitive film provided on a substrate. To transfer a fine pattern having a minimum width which approximates the resolution limit of the projection aligner, a technique has been proposed for producing a phase difference between light beams passing through two adjacent apertures having a fine opaque pattern segment therebetween. A conventional method of forming a pattern so that the above phase difference is produced, is discussed in an article entitled "Improving Resolution in Photolithography with a Phase-Shifting Mask" by Mark D. Levenson et. al. (IEEE Trans. on Electron Devices, Vol. ED-29, No. 12, 1982, pages 1828 to 1836). According to the pattern forming method proposed in the above article, exposure beams having passed through two adjacent apertures with a fine opaque pattern segment therebetween are 180.degree. out of phase with each other. This method is suitable for improving the resolution of a pattern made of periodically arranged pattern segments.
The above-mentioned prior art is effective in improving the resolution of a pattern where two adjacent transparent apertures are isolated from each other by a fine opaque pattern segment. However, where the adjacent transparent apertures are connected at a position to form, for example, a U-shaped aperture pattern segment, it is impossible to produce a phase difference between exposure beams on both sides of the fine opaque pattern segment. Thus, in this situation it is impossible to form a circuit pattern an improved resolution.
Further, in many cases, the circuit pattern of a solid-state device or electronic device is formed so that end faces of adjacent linear aperture pattern segments are connected with each other. When the conventional pattern forming method for producing the phase difference is applied to such a circuit pattern, the phase of exposure light is abruptly changed at a portion of, for example, a U-shaped aperture pattern segment. Thus, the resolution of that part of the U-shaped aperture pattern segment where linear patterns are parallel to each other, is improved, but the U-shaped aperture pattern segment is separated into two parts. As a result, it becomes impossible to form a desired, united aperture pattern segment on a wafer.